One of the challenges when weaving is to choose the 'best' yarn for your project.
The first question I ask myself is, what kind of cloth do I want to make? What 'job' does it need to do?
Then I ask myself the density (epi/ppi), along with weave structure. Then I work out the design, and if I will use more than one weft colour (either within the warp, or just to make multiple things in different colours) and how will those colours be arranged if more than one will be used.
A new weaver can follow a 'recipe' and generally wind up with good results. But here's the thing - yarn is not limited when it comes to the kind and quality it comes in.
It is particularly confusing when a large segment of weavers use knitting terms to describe their yarn. Or that they don't understand how yarn is made - how it is prepared for and then spun - are the fibres parallel or jumbled; how many twists per inch per ply (if there is more than one) and how tightly twisted the yarns are.
Twist imparted to the yarn is going to change the characteristics the yarn will have. Spinning loosely will mean a yarn will wear less well than the same fibres, treated the same way, spun with more twist.
There are two commonly available cotton yarns, repeatedly used but little understood. The version of 2/8 I prefer is prepared with the fibres parallel, then given a higher degree of twist in the spinning, which is then countered during the plying so that the yarn is relatively 'balanced' - in other words, not a huge degree of twist energy left in the yarn. The other yarn, much more commonly available in the US is 8/2. The fibres are mixed well, then open end spun. This version of the yarn has the same yards per pound as the 2/8, which makes it 3360 yards per pound, but the yarn is lofty, slightly thicker than the 2/8, less strong, and more absorbent than the 2/8.
To look at them, they don't really look all that different. I had to change the photo to black and white for the difference to begin to be visible to the eye.
If you don't know about these differences, you might find yourself disappointed in your results. If you use the 8/2 as warp, you may find that it dusts off more than the 2/8, it might break more easily, it feels 'better' at a lower density - because it's slightly thicker than the 2/8.
And this kind of 'unseen' difference is why most yarn charts giving density are a range, plus weave structure being used.
Just recently I saw a conversation on a group where one person asked for epi for a yarn, and then had a variety of answers. I wanted to ask how the yarn had been spun; was it open end? Or ring spun?
Because these things matter. Until the weaver understands the basic production processes for their yarn, they are working in the dark (so to speak).
I go into this (and other characteristics) in more detail in The Intentional Weaver,* and the class at School of Sweet Georgia.
*In Canada you can buy the pdf version, in the US, the books are printed in the US so you can still purchase in spite of the Canada Post strike.